In a background art, there is known an exhaust system structure of an engine of covering an exhaust manifold by an insulator in order to prevent heat radiated from the exhaust manifold from effecting an influence on a part arranged at a surrounding thereof.
However, when the exhaust manifold is covered by the insulator, heat is confined at inside thereof, and therefore, it is necessary to radiate the heat at inside of the insulator to outside thereof, however, when the heat is radiated to outside of the insulator from a vicinity of a portion of attaching the exhaust manifold to the engine, there poses a problem that a cylinder head gasket interposed between a cylinder head and a cylinder head cover constituting the engine or a member present at a surrounding thereof is thermally deteriorated.
Hence, as shown by FIG. 4, there is proposed a structure providing a clearance S for radiating heat between an engine 104 at a vicinity of an attaching portion of an exhaust manifold 102 and an insulator 106 and providing a heat shielding portion 112 of shielding heat by guiding heat from the clearance S in a direction of being remote from the engine 104 and reaching the engine 104 (refer to, for example, JP-A-2002-276358).
There is a case in which the heat shielding portion 112 is integrally provided to an exhaust manifold gasket 110 interposed between the exhaust manifold 102 and the engine 104 in order to achieve a reduction in a number of parts and a number of integrating steps.
The exhaust manifold gasket 110 includes a gasket main body 114 comprising a metal plate having an elasticity of stainless steel or the like and shielding a bonding face of the engine 104 and the exhaust manifold 102, and a base plate 116 comprising a metal plate of a steel plate or the like and fixing the gasket main body 114, the heat shielding portion 112 is extended integrally from the base plate 116 to a side of the exhaust manifold 104, and therefore, there is a concern of vibrating the heat shielding portion 112 extended in a flange-like shape by a vibration generated from the engine 102 and generating noise, which is problematic.
In addition thereto, meanwhile, there is a case of providing a secondary air supply apparatus of supplying secondary air to an exhaust system of an engine in order to promote oxidation of an exhaust gas.
As shown by FIG. 5, the apparatus 120 is constituted to supply secondary air cleaned by an air cleaner or the like to a secondary air introducing path 123 by way of a secondary air supply flow path 124 by an electric type air pump or the like and introduce the secondary air from the secondary air introducing path 123 to an exhaust port 122 of an engine 125.
The secondary air introducing path 123 is formed as a through hole penetrating from a side wall 121a of a cylinder head 121 to the exhaust port 122 one by one for respective cylinders of the engine 125 in order to achieve promotion of a reflammability of the exhaust gas and has a structure of introducing the secondary air directly to the exhaust port 122.
On the other hand, the secondary air supply path 124 is a path for distributing to supply the secondary air to the secondary air introducing paths 123 and is provided along the side wall 121a of the cylinder head 121.
There are present engines which are provided with and not provided with the secondary air supply apparatus 120, by reason of restraining a fabrication cost in fabricating the engines, there is a case of using a common cylinder head, that is, the cylinder head 121 provided with the secondary air introducing path 123 communicated with the exhaust port 122 at the side wall 121a. 
In such a case, in the engine 125 which is not provided with the secondary air supply apparatus 120, as shown by FIG. 6, the secondary air introducing path 123 provided at the cylinder head 121 is opened to an outer side, and the opening portion is sealed by an exhaust manifold gasket 127 interposed between the opening portion and an exhaust manifold 128.
However, the exhaust gas generated at the exhaust port 122 impinges on the exhaust manifold gasket 127 by way of the secondary air introducing path 123, and therefore, there poses a problem that noise is liable to be generated by vibrating the exhaust manifold gasket 127.
Hence, the invention has been carried out in view of the problems and it is an object thereof to provide a gasket which is difficult to generate noise by restraining a vibration in a gasket interposed between a cylinder head and an exhaust manifold of an engine.